Results 1 - 10 of 554
Results 1 - 10 of 554. Search took: 0.021 seconds
|Sort by: date | relevance|
[en] Even after more than 160 years of observations and modelling of solar prominences their true nature contains many open questions. In this work we argue that current 2D prominence fine structure models can help us to understand the puzzling connection between quasi-vertical fine structures often seen in quiescent prominences observed on the solar limb and horizontally aligned dark fibrils representing the fine structures of prominences observed in absorption against the solar disk (filaments).
[en] The EXAFS spectra of Cu and Pd foil from many different beamlines and synchrotrons are compared to address the dependence of the amplitude reduction factor (S02) on beamline specific parameters. Even though S02 is the same parameter as the EXAFS coordination number, the value for S02 is given little attention, and is often unreported. The S02 often differs for the same material due to beamline and sample attributes, such that no importance is given to S02-values within a general range of 0.7 to 1.1. EXAFS beamlines have evolved such that it should now be feasible to use standard S02 values for all EXAFS measurements of a specific elemental environment. This would allow for the determination of the imaginary energy (Ei) to account for broadening of the EXAFS signal rather than folding these errors into an effective S02-value. To test this concept, we model 11 Cu-foil and 6 Pd-foil EXAFS spectra from around the world to compare the difference in S02- and Ei-values.
[en] In this brief work we investigate any possible variation of the fine structure constant at the epoch of recombination. The recent measurements of the Cosmic Microwave Background anisotropies at arcminute angular scales performed by the ACT and SPT experiments are probing the damping regime of Cosmic Microwave Background fluctuations. We study the role of a mechanism that could affect the shape of the Cosmic Microwave Background angular fluctuations at those scales, namely a change in the recombination process through variations in the fine structure constant α
[en] We calculate the Zeeman-fine energies of atomic potassium by using the energy eigenvalues for hydrogen-like atoms for n < 11. We find 18 different energy values and 153 wavelengths some of which are the same. The calculated wavelengths are in good agreement with the observed values for potassium atom.
[en] Black hole apparent horizons possess a natural notion of stability, whose spectral characterization can be related to the problem of the stationary quantum charged particle. Such mathematical relation leads to an “analyticity conjecture” on the dependence of the spectral properties on a complex “fine-structure-constant” parameter, that can reduce the study of the spectrum of the (non-selfadjoint) MOTS-stability operator to that of the (selfadjoint) Hamiltonian of the quantum charged particle. Moreover, this perspective might open an avenue to the spinorialtreatment of apparent horizon (MOTS-)stability and to the introduction of semiclassicaltools to explore some of the qualitative aspects of this black hole spectral problem. (paper)
[en] Study of accurate resonant features of O II is crucial in predicting its abundances in nebular plasmas and for its diagnostic role. A well known large discrency exists in the predicted abundance of the ion depending on the radiative or collisional processes taken in to consideration. We will report new calculations for resonant structures in photoionization of O II where we have noted important features not seen before, especially in the low-energy region of the three fine structure components of 2s22p23P of core O III. These are expected to make considerable differences in the low temperature recombination. Preliminary comparison of the new results with experiments shows improved agreement.
[en] A series of photodetachment spectra from O- has been measured from near threshold to several eV using the technique of velocity-map imaging. With a resolving power of ΔE/E ≤ 0.38%, the energy and angular dependences for the six fine-structure transitions have been determined. For the first time, the energy and angular dependences of the cross section within a few meV of threshold have been determined.
[en] We examine the dynamical characteristics of massive interacting scalar field introduced in the Bekenstein-Sandvik-Barrow-Magueijo (BSBM) theory. Based on the classification of matter- and radiation-dominated cosmological eras, we consider three possible physical scenarios that allowed by the theory. We present the analysis of its dynamics in terms of phase space of the corresponding massive scalar field. The results demonstrate distinct characteristics between those eras. Characteristic of the related fine structure constant is also discussed. (paper)
[en] GNXAS is a suite of programs based on multiple scattering calculations which performs a structural refinement of EXAFS spectra. It can be used for any system although it has been mainly developed to determine the local structure of disordered substances. We developed a user-friendly graphical user interface (GUI) to facilitate use of the codes by using wxPython. The developed GUI and the codes are multiplatform running on Windows, Macintosh and Linux systems, and are free shareware (http://gnxas.unicam.it). In this work we illustrate features and potentials of this newly developed version of GNXAS ( w -GNXAS). (paper)
[en] An EXAFS expression was introduced for analysis of positive or negative thermal expansion. The EXAFS parameters were directly related to the interatomic potential. Also, it was shown that the sign of anharmonic potential parameter k3 depends on the sign of thermal expansion coefficient. Simulation works showed that the positive or negative thermal expansion can be sensitively measured by EXAFS study.